In recent years, safety awareness has been enhanced as a common problem to be solved in the car industry and a further improvement of wet grip performance and steering stability is required. Various studies have been done so far for improving wet grip performance and many inventions of a rubber composition comprising silica have been reported. Since tire performance depends on various factors such as a tire structure or a material to be used for tire and strongly depends on performance of a rubber composition particularly at a tread portion contacting a road surface, a technical improvement of a rubber composition for tire such as a tread has been widely considered and put into practical use.
Because of the technical improvement of a rubber composition for tread comprising silica, a significant progress is brought to wet grip performance of a tire. On the other hand, steering stability has not been improved sufficiently and has room for improvement. In particular, a performance change with respect to a temperature change due to running at a high temperature region or a performance change with respect to a case where a road surface change such as from a wet road surface to a dry road surface is occurred remains an important technical problem to be solved and has room for improvement. Additionally, though many studies have been done with respect to temperature dependence or dependence on road surface of a rubber composition at an extremely low temperature region which is a use environment of snow tires, such dependence at a high temperature region such as a dry road surface is not considered.
In JP 2006-056919 A, JP 2007-197671 A and JP 2008-101158 A, there is disclosed a rubber composition for tire comprising a predetermined amount of a predetermined diene rubber and silica, but a control of a performance change (temperature dependence and dependence on road surface) at a high temperature region such as a dry road surface is not considered. Further, though JP 2011-089081 A discloses a rubber composition which can decrease temperature dependence of hardness, a performance change with respect to a road surface change from a wet road surface to a dry road surface is not considered.